The hailstorms, strong winds and rains fell over Guangdong province, next to Hong Kong, at the weekend.
Provincial flood control officials told Xinhua news agency and the China Daily newspaper that gales had been as strong as 45.5m (50 yards) per second.
Most of the victims of the weather were killed when walls and work sheds collapsed in the strong winds.
Objects flying or falling from buildings also caused some deaths, officials said.
More than 100 people have been injured.